Construction of aircraft sustaining rotors



March 21, 1939. A E LARSEN 2,151,216

CONSTRUCTION OF AIRCRAFT SUSTATNTNG ROTORS Filed April 50, 1938 ATTORNEYJ.

Patented Mar. 21, 1939 CONSTRUCTION OF AIRCRAFT SUSTAINING ROT OBS

Agnew E. Larsen, Jenkintown, Pa., assignor, by mesne assignments, to Autogiro Company of America, a corporation of Delaware Application April 30, 1938, SerialNo. 205,228

13 Claims.

This invention relates to aircraft sustaining rotors, especially of the type in which the rotor blades are mounted for swinging movements during flight and also for pitch change movement.

While certain features of the invention are applicable to the helicopter type of machine incorporating a rotor adapted to be power driven in ight, the invention is particularly useful in a machine of the type in which the rotor is adapted for autorotative actuation in normal night, provision being made for reduction of the blade pitch from the autorotative setting to the substantially zero setting during driving of the rotor prior to take-H. This type of take-off, sometimes referred toas jump or direct take-off, involves driving of the rotor to a speed higher than the normal autorotational rate, with the blades at substantially no lift or zero pitch setting, in order to store a substantial quantity of kinetic energy in the rotor, which is subsequently released, after disconnection of the rotor driving clutch, by increasing the blade pitch from the substantially zero value either to the normal autorotative value or higher than that value, whereby 25 to develop a high initial thrust for raising the machine from the ground. A craft capable of this .general type of operation is shown in copendng application of James G. Ray, Serial No. 91,838, filed July 22, 1936. u

The features of improvement of this invention are concerned with blade mounting mechanism providing for pitch change movement of the blade to accomplish this general type of direct take-off and flight, the mounting mechanism further providing novel means for accommodating the blade oscillations set up as a result of night forces, especially oscillations generally within the rotative path of travel of the blades.

More specifically, the invention provides a 40 blade mounting permitting some limited degree of rotation of the blade substantially about its own longitudinal axis to effect pitch change, this movement being resisted by resilient means interconnecting certain of the blade mounting parts,

lll

' 45 which resilient means further serves the purpose of'accommodating lag-lead oscillations of the blade in its rotative path of travel.

In addition to the above, the invention has in view the provision of means acting-under the influence of centrifugal force for ensuring that the blade during normal autorotative flight shall remain at the desired autorotative pitch setting.

- According to another feature of the invention, while certain blade mounting parts are inter- 55 connected by means of a resilient element as (Cl.l 244-18) aforesaid, means are provided to relieve the resilient element from the centrifugal load on the blade during rotation.

How the foregoing objects and advantagesare accomplished, together with others which will occur to those skilled in the art, will appear more fully in the following description, referring to the accompanying drawing, in which- Fig. 1 is a plan view, with parts in horizontal section, of a rotor hub and the 'root end portion of a blade mounted thereon;

Fig. 2 is a side view of the mechanism shown in Fig. 1, certain parts being here shown in vertical section on the line 2-2 applied to Fig. 3, and

Fig. 3 is a View taken substantially as indicated by the section line 3-3 of Fig. 2.

In considering the drawing and the features shown therein, it should be kept in mind that the craft preferably is equipped with a. forward propulsion engine and propeller and with a disconnectible drive mechanism extended from the engine to the rotor hub for the purpose of driving the rotor prior to take-off in accordance with the operation hereinbefore referred to. Still further, it should be noted that preferably the machine incorporates some system of direct control,

which may take the form of a tiltable mounting for the hub providing for shift of the lift line of the rotor in all directions with respect to the center of gravity of the craft, in the general manner disclosed, for example, in the copending application of Juan de la Cierva, Serial No. 645,985, filed December 6, 1932.

While the rotor may incorporate any desired number of blades, the embodiment illustrated in- 3 corporates a hub 4 constructed for a three-bladed rotor, there being three apertured lugs 5 projecting from the hub, one for each blade. One of the blades is shown in Figs. l and 2 as being attached to the lug 5 at the right-hand side of the hub, the root end portion of or root end fitting for the `blade spar being shown at 6. This member 6 extends within the sleeve l having an enlargement .8 at its inner end adapted to be threaded or otherwise connected with the member 9 carrying a pair of spaced apertured ears Ill-I0 which embrace the hub lug 5 and which are connected with this lug by means of a pivot Il, preferably positioned to provide at least some degree of freedom for blade oscillation in a direction perpendicular to the mean rotative path of travel of the blades.

At its inner end the root end member 6 of the blade is provided with an enlargement or abutment i2 of special configuration, the outer side direction.

thereof being provided with angularly arranged bearing faces I3 joined in a ridge I4, the axis of which substantially parallels the hub axis when the blade is in true radial position. The enlargement 8 at the inner end of the sleeve 1 is provided with a cooperating socket having angular surfaces I5 joined in the apex of a trough in which the ridge Il seats.

Intervening between the root end fitting 6 and the sleeve 1 is a resilient or rubber sleeve I6, this sleeve preferably, although not necessarily in all embodiments, being cemented, vulcanized, or otherwise bonded to both of members 8 and 1.

From examination of Figs. 1 and 2 it will be apparent that this blade root mounting provides freedom for resiliently cushioned oscillative movement of the blade about the axis of ridgej I4, the angle included'in the V of the surfaces Il being smaller than the angle included in the V of the surfaces I5. The resilient element or sleeve I6 is of such length, thickness and material as to provide for relative rotation of members 6 and 1 substantially about the longitudinal axis of the blade, which relative rotation is accompanied by torsional deformation of the resilient element 6. With the resilient element bonded to both of the members, upon torsional deformation thereof, a restoring moment is set up, tending to return the blade, and'it is here noted thatthe neutral point of this restoring moment coincides with theA relative posltionof the partsin which the ridge I 4 is seated in the trough of surfaces I5. In other words, when the ridge I4 is seated in the trough of surfaces I5, the resilient element I6 exerts no force tending to turn the blade in either The position of the parts just mentioned further corresponds to a lift incidence position of the blade (indicated by the outline shown in dashes at I1 in Fig. 3) Within the normal autorotational range, for example, in the neighborhood of 5. The blade may be moved from this position to the substantially zero incidence position indicated by the dot and dash outline I8' in Fig. 3, for which purpose the abutment I2 at the inner end of the blade root tting 6 is provided with an upwardly projecting arm I9 extending through an aperture in the socket 8. `The arm may be moved by means of a cylinder and piston device 20-2I, the piston transmitting its movement to the lever I9 by means of the stem 22 which is pivotally connected with the lever I9 as at 23. The cylinder 20 is mounted on a-supporting bracket or the like 24 which is rigid with the socket 8 and, therefore, with the sleeve 1 and the attachment part 9. The cylinder may be supplied with fluid pressure, preferably hydraulic, through the connection 25, the pressure being controlled in any suitable manner, for instance, -under the inuence of an interlock with the clutch control for the rotor driving mechanism as disclosed, for example, in the copending application of James G. Ray, Serial No. 91,838, referred to above.

Movement of the lever I9 toward the right when viewed as in Fig. 3 may be limited by the forward end 26 of the slot through which` this lever projects, the arrangement desirably providing for location of this end of the slot at a position corresponding to the zero lift position I8 of the blade. The other end 21 of the slot just mentioned may be employed, if desired, as a` stop limiting movement of the blade in the positive pitching direction.

From inspection of Figs. 1 and 2 it will be seen that upon rotation of the blade root. iltting 5 within the sleeve 1, the ridge I4 will ride up somewhat on the inclined surfaces I5, with the result that the blade will be drawn radially inwardly' when it is moved to the zero incidence position. Because of the inclination of the surfaces I5, the

kaction of centrifugal force on the blade tends to return the ridge I 4 to the position shown in Fig. 1, in which this ridge seatsfin the trough formed between the surfaces I5. In this way means are'provided for positively returning the blade from the zero to the normal autorotative pitch position under the influence of centrifugal force.

The action of the device described is, therefore, as follows:

Assuming that the craft is on the ground and preparations are being made for effecting takeoif, the rotor drive is engaged and fluid pressure admitted to cylinder 20, in consequence of which the blade is moved to the zero incidence position (I8 in Fig. 3). The driving is preferably continued until the speed of rotation is substantially in excess of the normal autorotative speed whereupon the rotor driving clutch is disconnected and the pressure in cylinder 20 relieved, in consequence of which the blade moves from the zero pitch position to the autorotative value under the influence of two forces-first, the action of back into the trough of surfaces I5 and, second,

the torsional force of the rubber sleeve I6 intervening between sleeve 1.

With regard to the foregoing, it may be noted that it has been customary in many rotorsof the general character here involved to provide a generally upright or vertical drag pivot about which the blade is free to oscillatefwithin the plane ofrotation. It has been found, however, that the degree of oscillation in this plane normally is not very great, in consequence of which lateral distortion of the resilient element I8 in the construction illustrated is adequateto accommodate such drag oscillations. 1

The construction of this invention is also of advantage since it avoids excessive lag or lead oscillations of the blade during driving prior to take-olf and at the same time provides the required degree of freedom of oscillation for iiight purposes.

In order to ensure the desired action as described above, the angle of surfaces I5 is preferably not greater than about 15 from a plane perpendicular to the longitudinal axis of the blade.

From the above it will be seen that the inveny tion provides a blade mounting mechanism incorporating a resilient element which is preferably interconnected with orl bonded to a pairl of relatively rotatable blade monuting parts, the resilient element being distortable in several different senses (for example, torsionally and latlelement of the centrifugal load of the blade under all conditions of operation, even with the blade in different pitch positions.

Attention is called to the fact that certain features disclosed herein are also disclosed and are claimed in copending application 184,914 of Paul the blade root fitting 6 and the H. Stanley, filed January 14, 1938; or incopending application 183,925 of Harold F. Pitcairn, filed January 8, 1938, both of said copending applications having been assigned .to the' assignee of the presentapplication.

I claim:

1. In an aircraft sustaining rotor having a hub and a blade, mechanismv for mounting the blade on the hub including pair lof telescopically associated members arranged with'their axes substantially in alignment withthe longitudinal blade axis, an interposed cylindrical resilient sleeve bonded to both of said members and providing freedom for relative rotation of said members to vary the pitch setting of\the blade, and controllable means for effecting relative rotation of said members.

2. In an aircraft sustaining rotor having a hub and the blade, mechanism for mounting the blade on the hub including a pair of telescopically associated members arranged with their axes substantially in alignment with the longitudinal blade axis, an interposed cylindrical resilient sleeve bonded to both of said members and providing freedom for relative rotation of said members to vary the pitch setting of the blade, controllable means for effecting relative rotation of said members in vone sense, and means operative under the influence of centrifugal force on the blade for effecting relative rotation of said members in the opposite sense.

3. In an aircraft sustaining rotor having a hub and a bla'de, mechanism for mounting the blade on the hub including a pair of telescopically associated members arranged with their axes substantially in alignment with the longitudinal blade axis, an interposed cylindrical resilient sleeve 'bonded to.both of' said members and providing freedom for relative rotation of said members to vary the pitch setting of the blade, controllable means for effecting relative ro'tation of said members in a sense providing movement of the blade from a higher to a lower pitch position, and means operative under the influence of centriiugal force on the blade for effecting relative rotation of said members in the opposite direc- 4. In an autorotatable sustaining rotor having a hub and blade, mechanism for mounting the blade on the hub including a pair of members relatively rotatable substantially about the longitudinal axis of the blade, a resilient element interconnecting said members, the resilient element being torsionally distortable to provide freedom for pitch change movement of the blade upon relative rotation of said members, and

means operative under the influence of centrifu-y gal force for urging said members toward that relative position in which the pitch setting of the blade lies within the autorotative range.

5.r In an autorotatable sustaining rotor having a hub and blade, mechanism for mounting the blade on the hub including a pair of members relatively rotatable substantially about the longitudinal axis of the blade, a resilient element inter-r connecting said members, the resilient element being torsionally distortable to provide freedom for pitch change movement of the blade upon relative rotation of said members, and means relieving said resilient element of the centrifugal' load on the blade during rotation.

6. In an autorotatable sustaining rotor having a hub and blade, mechanism for mounting the blade on the hub including a pair' of members relatively rotatable substantially about the longitudinal axis of the blade, a resilient element interconnecting said members and. bonded to both of them, the resilient element being torsionally distortable to provide freedom for pitchchange movement of the blade upon relative rotation of said members, and means operative under the influence of centrifugal force for urging said members toward that relative position in which the pitch setting of the blade lies within the autorotative range, said element being bonded to said members in such positionvthat substantially no torsional moment tending toward rotation of said members is present when said members are in the position aforesaid.

7. In an autorotatable sustaining rotor having a hub and a blade, mechanism for mounting the blade on the hub including a pair of members relatively rotatable substantially about the longitudinal. axis of the blade, a resilient element interconnecting said members, the resilient element being torsionally distortable `to provide freedom for pitch change movement of the blade upon relative rotation of said members, means operative under the influence of centrifugal force for urging said members toward that relative position in which the pitch setting of the blade lieswithin the autorotative range, and controllable means for relatively rotating said members to a position in which the blade is at substantially zero pitch.

8. In a bladed aircraft sustaining rotor, a blade `mounting mechanism including an abutment at the root end of the blade having a ridge thereon with its axis extended at an angle to the longitudinal axis of the blade, a cooperating socket having a trough in which said ridge is received, providing freedom for oscillation of the abutment and therefore of the blade substantially about the axis of said ridge with respect to the socket, and a resilient element interconnecting the socket and theblade.

9. In a bladed aircraft sustaining rotor, a blade mounting mechanism including an abutment at the root end of the blade having a ridge `thereon with its axis lying in a plane generally transverse to the longitudinal axis of the blade, a cooperating socket having a trough in which said ridge is received, providing freedom for oscillation of the abutment and therefore of the blade substantially about the axis of said ridge with respect to the socket, and a resilient element interconnecting the socket and the blade, said resilient element being torsionally distortable to provide freedom for pitch change movement of the blade with respect to the socket.

l0. In a bladed aircraft sustaining rotor, a blade mounting mechanism including an abutment at the root end of the blade having a ridge thereon with its axis lying in a plane generally transverse to the longitudinal axis of the blade, a cooperating socket having a trough in which said ridge is' received, providing freedom for oscillation of the abutment and therefore of the blade substantially about the axis of said ridge with respect to-the socket, a resilient element interconnecting the socket and the blade, said resilient element being torsionally distortable to provide freedom for pitch change movement of the blade with respect to the socket, and controllable means for rotating the blade and abutment with respect to the socket,

11. In an aircraft sustaining rotor having a hub and a blade, mechanism for connecting the blade with the hub including a pair of telescopically arranged mounting members positioned the two blade mounting members substantially about an axis at the apex of the V-shaped sur- `face s,`an d yielding means interposed between said membersfor resisting said rocking.

. l2. In'an aircraft sustaining rotor having a hub and a blade, mechanism for connecting the blade Vwith the hub including a pair of telescopically arranged mounting members positioned with their` with their axes substantiallyin-alignment with the f .longitudinal axis of the blade, said members hav- Y ing `gcooperatix'lg complementary abutment' and socket parts through which the centrifugal load on the-blade is transmitted to the hub,rthe beara ing surfaces-of said parts respectively being oi' convex and concave V-shape, with a smaller angle Y included in the V of the convex part than in the' V of the concave part to provide freedom for relative 'rocking' of the two parts and. therefore, of

races/oi said parts respectively beingv of convex "and .concavevV-shape, with 'a lsmaller angle included in the `V ofthe convex part'than-in the V of the concave part .to provide freedom for relative rocking of the two parts and, therefore, of the two blade mounting members substantially about an axis at the lapex of the V'shaped surfaces.. and yielding means interposed between' said members for resisting said rocking, said' yielding means being torsionally distortable substantially about' the longitudinal axis of the blade, and means for relatively rotating said members and said parts to eect blade pitch change.

/b 13. In an aircraft sustaining rotor incorporating a hub and a blade. blade mounting mechanism including a resilient element interconnecting the blade and the hubwand. providing freedom for blade oscillation and blade pitch Achange movement by distortion of said element, .and means for relieving said element'of the centrifugal load on the blade during rotation. l

4AGI'NEW n. LaRsEN. 

